1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having a column spacer and method for fabricating the same.
2. Discussion of the Related Art
Demands for various display devices have increased with development of an information society. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), electroluminescent displays (ELDs), and vacuum fluorescent displays (VFDs). Some of the flat display devices have already been applied to displays for various equipments.
Among the various flat display devices, liquid crystal display (LCD) devices have been most widely used due to their advantageous characteristics such as thin profile, lightweight and low power consumption, and thus are substituting for Cathode Ray Tubes (CRTs). In addition to mobile type LCD devices such as LCD devices for notebook computers, LCD devices have been developed for computer monitors and televisions to receive display broadcasting signals.
In order to use LCD devices in various fields as a general display, LCD devices should offer a high quality picture, such as a high resolution and high luminance with a large-sized screen, while still maintaining such characteristics as lightweight, thin profile and low power consumption.
A general LCD device includes first and second substrates bonded to each other with a certain space, and a liquid crystal layer formed between the first and second substrates.
The first substrate includes a plurality of gate lines arranged along a first direction at fixed intervals and a plurality of data lines arranged along a second direction perpendicular to the first direction at fixed intervals. A plurality of pixel regions are defined by the gate and data lines. A plurality of pixel electrodes are arranged within the pixel regions. A plurality of thin film transistors are formed at regions where the gate lines cross the data lines and apply data signals of the data lines to the pixel electrodes in accordance with signals applied to the gate lines.
Also, the second substrate includes a black matrix layer for preventing a light leakage from portions of the first substrate except at the pixel regions, R/G/B color filter layers for displaying various colors, and a common electrode for producing images on the color filter layers.
The liquid crystal layer is formed between the first and second substrates. The molecules of the liquid crystal layer are driven by an electric field generated between the pixel electrode and the common electrode. Light passing through the liquid crystal layer is controlled by the alignment direction of the molecules of the liquid crystal layer, thereby displaying images. This type of LCD device is referred to as a twisted nematic (TN) mode LCD device, which has disadvantageous characteristics such as a narrow viewing angle. In order to overcome the narrow viewing angle, an in-plane switching (IPS) mode LCD device has been developed.
In the IPS mode LCD device, a pixel electrode and a common electrode are formed on the first substrate in parallel to each other at a fixed interval, so that the pixel electrode and the common electrode generate an IPS mode electric field (horizontal electric field) that aligns the molecules of the liquid crystal layer.
Meanwhile, a plurality of spacers are formed between the first and second substrates of the aforementioned LCD devices to maintain a constant cell gap for the liquid crystal layer. The spacers may be ball spacers or column spacers.
The ball spacers have a spherical shape and are dispersed on either the first or second substrates. Also, the ball spacers are relatively free in their movements even after the first and second substrates are bonded to each other. The ball spacers have a small contact area with the first and second substrates.
By contrast, the column spacers are formed by an array process on the first substrate or the second substrate. The column spacers are formed on a predetermined substrate in a column shape with a predetermined height. Therefore, the column spacers have a relatively large contact area with the first and second substrates.
FIG. 1 is a sectional view illustrating an LCD device provided with a plurality of column spacers according to the related art.
Referring to FIG. 1, the LCD device provided with a plurality of column spacers includes first and second substrates 30 and 40 opposing each other, a column spacer 20 formed between the first and second substrates 30 and 40, and a liquid crystal layer (not shown) filled between the first and second substrates 30 and 40. The column spacer 20 is located corresponding to a predetermined position of the gate line 31.
The first substrate 30 includes a gate line 31 crossing a data line (not shown) to define a pixel region, a thin film transistor TFT formed on a region where the gate line 31 crosses the data line, and a pixel electrode (not shown) formed in each pixel region. The first substrate 30 further includes a gate insulating layer 36 formed on the entire surface including the gate line 31 and a passivation layer 37.
The second substrate 40 includes a black matrix layer 41 corresponding to a region other than the pixel region, a stripe shaped color filter layer 42 corresponding to vertical pixel regions parallel with the data line, and a common electrode or an overcoat layer 43 formed on the color filter layer 42.
FIGS. 2A and 2B are a plan view and a sectional view illustrating a touch defect of the related art LCD device provided with a plurality of column spacers.
Referring to FIGS. 2A and 2B, when an LCD panel 10 provided with a plurality of column spacers is touched with a finger or other object, a spot is generated on the touched portion. This spot is referred to as a touch spot or touch defect because the spot is generated on the screen of the LCD panel.
As described above, the column spacers form a relatively large contact area with the substrates in an LCD device, compared with the ball spacers. As illustrated in FIG. 2B, such a large contact area between the column spacers 20 and its opposing first substrate 1 generates a frictional force when the LCD device is touched with a finger or other object, and the frictional force shifts the relative positions of the first and second substrates I and 2, creating the aforementioned touch defect. Once such a touch defect is created, it takes a long time for the LCD device to restore the original state of the first and second substrates 1 and 2. For this reason, the touch spot remains on the LCD screen until the first and second substrates 1 and 2 are restored to their original state.
The aforementioned related art LCD device provided with the column spacers has the following problems.
First, as described above, when the LCD device is touched with a finger or other object, the touch spot is created and remains on the LCD screen until the first and second substrates 1 and 2 are restored to their original state.
Second, when the LCD device is arranged in a vertical direction under a high temperature environment, liquid crystal inside the LCD device is thermally expanded. In the worst case, the cell gap of the LCD device increase to a thickness greater than the height of the column spacers, so that the liquid crystal flows into the space between the column spacers and its opposing substrate and are then concentrated on a lower corner of the LCD device arranged in a vertical direction, thereby causing an opaque spot.
Finally, in addition to the frictional force between the column spacers and its opposing substrate, the touch defect is generated when liquid crystal is not sufficiently provided inside the LCD device. By contrast, when liquid crystal is excessively provided inside the LCD device, a gravity defect is generated. Accordingly, it is important to provide a proper amount of liquid crystal to fabricate an LCD device free from the touch and gravity defects. Due to the structure of the related art LCD device, a range of amount of liquid crystal is limited in fabricating an LCD device free from the touch and gravity defects.